Producers and Energy
A plant makes sugar, and a caterpillar eats the plant. Which organism is the producer?
The plant, because it makes its own food.
A plant has sunlight and water. Which reactant is missing for making sugar?
CO2
Which organelle would you examine to study photosynthesis in a leaf cell?
The chloroplast.
What is the main job of the light-dependent reactions: assembling sugars or capturing and transferring energy?
Capturing and transferring energy.
Which stage uses carbon dioxide to build molecules that contribute to sugar formation?
The Calvin cycle, or light-independent reactions.
Trace the energy in a panda’s food back to its original source.
Sunlight supplies energy that plants store in sugars. The panda obtains that chemical energy by eating plants.
Sensors around a plant show carbon dioxide decreasing and oxygen increasing. What does this suggest the plant is doing?
Photosynthesizing: taking in carbon dioxide and releasing oxygen.
Where inside a chloroplast would you find the photosystems that capture light energy?
In the thylakoid membrane.
Which two products carry energy from the light-dependent reactions to the Calvin cycle?
ATP and NADPH.
A plant has plenty of carbon dioxide but no available ATP or NADPH. Can its Calvin cycle continue building sugars? Explain.
No. It needs ATP and NADPH from the light-dependent reactions.
A student says plants “create energy” during photosynthesis. How would you correct this statement?
Plants transform light energy into chemical energy stored in sugar.
A student claims the oxygen released during photosynthesis comes from carbon dioxide. Which substance actually supplies that oxygen?
Water, which splits during the light-dependent reactions.
A scientist observes the Calvin cycle occurring outside the thylakoids. What region of the chloroplast is being observed?
The stroma.
Chlorophyll loses energized electrons after absorbing light. What replaces those electrons?
Electrons from water molecules that split.
Why is “dark reactions” a misleading nickname for the Calvin cycle?
The cycle does not directly require light, but it can occur in the light and depends on ATP and NADPH.
Some bacteria make sugars in an environment that receives no sunlight. What process could they use, and what supplies the energy?
Chemosynthesis, using energy from chemical compounds.
A plant builds new sugar molecules as it grows. Where does the carbon in those molecules originate?
Carbon dioxide from the atmosphere.
Why would a typical underground root cell have fewer chloroplasts than a leaf cell?
Underground roots generally receive little or no light, so their cells usually do not carry out photosynthesis.
Hydrogen ions move through ATP synthase. What useful molecule does this help produce?
ATP, formed by adding a phosphate group to ADP.
A model shows carbon dioxide entering a circular pathway and sugar leaving it. ATP and NADPH also enter. Which process does the model show?
The Calvin cycle.
Why would a major decrease in photosynthesis affect animals that never eat plants directly?
Their food chains depend on producers, and photosynthesis also supplies oxygen used in cellular respiration.
Write the balanced photosynthesis equation and identify the energy input.
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Light supplies the energy.
A diagram shows a thylakoid membrane containing photosystems, an electron transport chain, and ATP synthase. Which stage does it represent, and what evidence supports your answer?
The light-dependent reactions. Those structures capture light energy and produce ATP and NADPH.
A plant can produce ATP but cannot produce NADPH. What important contribution to sugar production would be missing?
The high-energy electrons supplied by NADPH.
Explain how sunlight captured in the thylakoid membrane eventually contributes to sugar production in the stroma.
The light-dependent reactions capture sunlight’s energy and produce ATP and NADPH. The Calvin cycle uses those molecules to help convert carbon dioxide into sugars.